Optical lens assemblies and related methods

ABSTRACT

The disclosed optical lens assemblies may include a pre-strained deformable element that exhibits a non-uniform mechanical strain or stress profile, a structural support element coupled to the pre-strained deformable element, and a deformable medium positioned between the pre-strained deformable element and the structural support element. Related head-mounted displays and methods of fabricating such optical lens assemblies are also disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional Pat.Application No. 17/160,169, filed Jan. 27, 2021, which is a continuationof U.S. Non-Provisional Pat. Application 16/018,746, filed Jun. 26,2018, which claims the benefit of U.S. Provisional Application No.62/650,254, filed Mar. 29, 2018, the entire disclosure of each of whichis incorporated herein by this reference.

BACKGROUND

Adjustable-lens systems may be useful in a variety of devices, includingeyeglasses, cameras, instrumentation, and virtual or augmented reality(“VR/AR”) systems, such as to adjust the focus of a display element(e.g., screen) or of a real-world image viewed by a user. One example ofan adjustable-lens system is a “liquid lens” assembly. As accommodativeelements, liquid lenses may be varifocal, may have high transmissivity,and with proper optical design can achieve low off-axis aberration anddistortion for high image quality over a range of optical powers.

Liquid lenses may often include a flexible membrane that is directlycoupled to a rigid backplane and a fluid that is disposed between therigid backplane and the membrane. Inducing a change in fluid pressuremay result in a convex or concave lens shape, which may be defined by aflexible membrane defining the lens shape. The lens shape formed by theshaped flexible membrane may not be ideal for some applications. Forexample, the edge of the lens may have a shape that is distorted byforces applied by attachments of the membrane to mechanical supportstructures. In addition, it may be difficult, expensive, or impossibleto customize the membranes to achieve desired optical properties, suchas to account for certain inter-pupillary distances or ophthalmiccorrections.

SUMMARY

As will be described in greater detail below, the present disclosuredescribes optical lens assemblies and head-mounted displays (“HMDs”)including deformable elements that may have a non-uniform strain orstress profile, as well as related methods.

In some embodiments, the present disclosure includes optical lensassemblies that include a pre-strained deformable element that mayexhibit at least one of a non-uniform mechanical strain or stressprofile, a structural support element coupled to the pre-straineddeformable element, and a deformable medium positioned between thepre-strained deformable element and the structural support element.

In some examples, the non-uniform mechanical strain or stress profilemay be a result of a variable pre-tension applied to the pre-straineddeformable element, and/or may be a result of residual stress within thepre-strained deformable element. The pre-strained deformable element mayinclude a central region and an edge region proximate a peripheral edgeof the pre-strained deformable element, and the pre-strained deformableelement may exhibit a mechanical strain or stress in the central regionthat is different than a mechanical strain or stress in the edge region.For example, the mechanical strain or stress in the central region maybe less than (e.g., at least about two percent less than) the mechanicalstrain or stress in the edge region. In some embodiments, the mechanicalstrain or stress in the central region may be greater than themechanical strain or stress in the edge region.

In some examples, the non-uniform mechanical strain or stress profilemay be configured to correct for at least a portion of a cylindricalerror of a user’s eye. The non-uniform mechanical strain or stressprofile may be based, at least in part, on an inter-pupillary distanceof a user. The non-uniform mechanical strain or stress profile may beconfigured to counter gravity sag in the pre-strained deformableelement. A display element may be positioned proximate to thepre-strained deformable element. When deformed, the pre-straineddeformable element may alter an optical property of the optical lensassembly.

In some embodiments, the present disclosure includes methods offabricating an optical lens assembly. In one example of such methods, atleast one of a non-uniform mechanical strain or stress profile may beinduced in a deformable element. The deformable element may bepositioned over a structural support element. A deformable medium may bedisposed between the deformable element and the structural supportelement.

In some examples, inducing the non-uniform mechanical strain or stressprofile in the deformable element may include at least one ofconditioning a material of the deformable element or stretching thematerial of the deformable element. Conditioning the material of thedeformable element may include thermoforming a polymer to a non-planarprofile. In further examples, conditioning the material of thedeformable element may include selectively exposing portions of thematerial of the deformable element to heat to induce residual strain orstress in the material of the deformable element, and/or selectivelypolymerizing portions of the material of the deformable element toinduce residual strain or stress in the material of the deformableelement. Stretching the material of the deformable element may includeat least one of uniaxially stretching the material, biaxially stretchingthe material, or stretching the material along at least one axis that isangled from vertical and horizontal relative to an intended orientationof the optical lens assembly when in use. When deformed, the deformableelement may alter an optical property of the optical lens assembly.

In some embodiments, the disclosed methods of fabricating an opticallens assembly may include determining a set of desired opticalproperties of the optical lens assembly for a user, providing adeformable element having a central region encompassing an optical axisand an edge region proximate a peripheral edge of the deformableelement, and inducing at least one of a non-uniform mechanical strain orstress profile in the deformable element. The non-uniform mechanicalstrain or stress profile may be selected to substantially obtain the setof desired optical properties. The deformable element may be positionedover a structural support element. A deformable medium may be disposedbetween the deformable element and the structural support element.

In some examples, the set of desired optical properties may include atleast one of a correction of at least one optical aberration, an opticalcentration location, or an ophthalmic correction. Inducing thenon-uniform mechanical strain or stress profile in the deformableelement may be performed before determining the set of desired opticalproperties of the optical lens assembly for the user. Providing thedeformable element may include selecting the deformable element with theinduced non-uniform mechanical strain or stress profile from a group ofdeformable elements with respective different mechanical strain orstress profiles.

In some examples, deformation of the deformable element positioned overthe structural support element may alter at least one optical propertyof the optical lens assembly. Inducing the non-uniform mechanical strainor stress profile in the deformable element may include at least one ofstretching a material of the deformable element, thermoforming thematerial of the deformable element to a non-planar profile, orselectively exposing portions of the material of the deformable elementto heat to modify residual strain or stress in the material.

Features from any of the above-mentioned embodiments may be used incombination with one another in accordance with the general principlesdescribed herein. These and other embodiments, features, and advantageswill be more fully understood upon reading the following detaileddescription in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate a number of example embodiments andare a part of the specification. Together with the followingdescription, these drawings demonstrate and explain various principlesof the present disclosure.

FIG. 1 is a cross-sectional side view of an optical lens assembly in anactuated state, according to an embodiment of the present application.

FIG. 2 is a cross-sectional side view of an optical lens assembly in anactuated state, according to another embodiment of the presentapplication.

FIG. 3 is a perspective view of an HMD according to an embodiment of thepresent disclosure.

FIG. 4 is a graph illustrating a pre-formed profile of a deformableelement of an optical lens assembly according to an embodiment of thepresent disclosure.

FIG. 5 is a graph showing principal strain values on an optical lensassembly after being pre-formed and uniformly stretched, according to anembodiment of the present disclosure.

FIG. 6 is a graph showing stress values on an optical lens assemblyafter being pre-formed and uniformly stretched, according to anembodiment of the present disclosure.

FIG. 7 is a plot showing reaction forces on a deformable optical elementat various dimple heights and for different directions of actuation,according to an embodiment of the present disclosure.

FIG. 8 is a plot showing a velocity of a deformable optical element atvarious dimple heights and for different directions of actuation,according to an embodiment of the present disclosure.

FIG. 9 is a plot illustrating a strain contour of an optical lensassembly according to an embodiment of the present disclosure.

FIGS. 10 and 11 are flow diagrams illustrating methods of fabricating anoptical lens assembly according to various embodiments of the presentdisclosure.

Throughout the drawings, identical reference characters and descriptionsindicate similar, but not necessarily identical, elements. While theexample embodiments described herein are susceptible to variousmodifications and alternative forms, specific embodiments have beenshown by way of example in the drawings and will be described in detailherein. However, the example embodiments described herein are notintended to be limited to the particular forms disclosed. Rather, thepresent disclosure covers all modifications, equivalents, combinations,and alternatives falling within the scope of the appended claims.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The present disclosure is generally directed to optical lens assemblies,HMDs, and related methods. As will be explained in greater detail below,embodiments of the present disclosure may include optical lensassemblies that include a deformable element having a non-uniformmechanical strain or stress profile. The non-uniform mechanical strainor stress profile may facilitate achieving desired optical propertiesupon deformation the deformable element. Methods of fabricating suchoptical lens assemblies and deformable elements include inducing anon-uniform mechanical strain or stress profile in the deformableelements, such as by pre-forming the deformable elements to have anon-planar shape, pre-stretching the deformable elements, and/orselectively heating at least a portion of the deformable elements, etc.Such methods may result in commercially feasible adjustable optical lensassemblies that may address conventional difficulties in customizationor achievement of certain optical properties.

The following will provide, with reference to FIGS. 1 and 2 , detaileddescriptions of example optical lens assemblies that include adeformable element that may have a non-uniform mechanical strain orstress profile. The description of FIG. 3 relates to an embodiment of anHMD that includes optical lens assemblies according to the presentdisclosure. With reference to FIGS. 4-9 , the following will providedetailed descriptions of strain profiles and other properties ofdisclosed optical lens assemblies. The discussion relating to FIGS. 10and 11 will provide detailed descriptions of various methods offabricating optical lens assemblies according to the present disclosure.

FIG. 1 shows a cross-sectional side view of an optical lens assembly 100in an actuated state. The optical lens assembly 100 may include aproximal optical lens subassembly 104 (also referred to as the “proximalsubassembly 104” for simplicity) for positioning close to a user’s eye,and a distal optical lens subassembly 106 (also referred to as the“distal subassembly 106 for simplicity) for positioning away from theuser’s eye. The optical lens assembly 100 may also include a housing 140(e.g., a frame element of an HMD) for supporting the optical lenssubassemblies 104, 106, which may at least partially cover a peripheraledge of the optical lens subassemblies 104, 106. The housing 140 mayalso support a display element 102 (e.g., an electronic display element,etc.) for displaying an image to the user. The display element 102 maybe positioned adjacent to and between the optical lens subassemblies104, 106.

The proximal subassembly 104 may include a rigid or semi-rigid proximalstructural support element 108 and a proximal deformable optical element110 (including a proximal deformable element 112 and a proximaldeformable medium 114) positioned over the structural support element108. In some examples, relational terms such as “over,” “on,”“downward,” “upward,” “highest,” “lowest,” etc., may be used for clarityand convenience in understanding the disclosure and accompanyingdrawings, and does not necessarily connote or depend on any specificpreference, orientation, or order, except where the context clearlyindicates otherwise. The proximal deformable element 112 may be directly(e.g., bonded, adhered) or indirectly (e.g., via a separate component ormaterial) coupled to the proximal structural support element 108.

As shown in FIG. 1 , in embodiments in which the proximal deformableelement 112 is directly coupled to the proximal structural supportelement 108, an outer periphery of the proximal deformable element 112may define an edge seal for containing the proximal deformable medium114 in a cavity defined between the proximal deformable element 112 andthe proximal structural support element 108. A force distributor ring150, which may also function as a pre-tension ring for maintaining apre-tension in the proximal deformable element 112, may be positionedover the proximal deformable element 112 proximate the outer peripheryof the deformable element 112. Similarly, the distal subassembly 106 mayinclude a distal structural support element 116 and a distal deformableoptical element 118 (including a distal deformable element 120 and adistal deformable medium 122). Another force distributor ring 150 may becoupled to the distal deformable element 120. The structural supportelements 108, 116 may be positioned on external sides of the opticallens assembly 100, and the deformable optical elements 110, 118 may bepositioned on internal sides of the optical lens assembly 100 facing thedisplay element 102.

Each of the structural support elements 108, 116, the deformableelements 112, 120, and the deformable media 114, 122 may besubstantially transparent to allow light to pass therethrough to an eyeof a user. Accordingly, at least portions of the structural supportelements 108, 116 and of the deformable optical elements 110, 118 may bepositioned in an optical aperture of the optical lens assembly 100,which may refer to a portion of the optical lens assembly 100 thatallows the passage of light to a user’s eye.

In some examples, the phrase “substantially transparent” may refer to anelement exhibiting greater than about 20% transmissivity and less thanabout 10% haze in the visible light spectrum. In some examples, the term“substantially,” in reference to a given parameter, property, orcondition may generally refer to a degree that one of ordinary skill inthe art would understand that the given parameter, property, orcondition is met with a small degree of variance, such as withinacceptable manufacturing tolerances. By way of example, depending on theparameter, property, or condition that is substantially met, theparameter, property, or condition may be at least 90% met, at least 95%met, at least 99% met, etc. In some examples, the phrase “deformableoptical element” may refer to an element (including one or morematerials or sub-elements) that is configured to be deformed to alter anoptical property (e.g., an accommodative property or an adaptive opticalproperty) of the optical lens assembly. In some examples, the term“accommodative” or “accommodation” may refer to changes in an opticalpower. In some examples, the term “adaptive” may refer to tunability forproviding control, compensation, and/or correction of wave front errorssuch as distortion and aberration(s). In some examples, “aberration” maygenerally refer to an optical image defect, including any deviation fromdiffraction-limited optical performance. Aberrations can be chromatic ormonochromatic and include, for example, tilt, defocus, astigmatism,coma, distortion, field curvature, spherical errors, cylindrical errors,etc.

The structural support elements 108, 116, deformable optical elements110, 118, and force distributor rings 150 may be coupled to andsupported by the housing 140 (e.g., an eyeglass frame element, an AR orVR headset frame element, etc.). In FIG. 1 , the deformable element 120and deformable medium 122 are shown in an actuated state, with anactuation force 160 acting on the force distributor rings 150 in adirection toward the user’s eyes. Because of the actuation force 160,the proximal deformable optical element 110 may have a convex shape toexhibit a positive-optical power, and the distal deformable opticalelement 118 may have a concave shape to exhibit a negative-opticalpower. In some embodiments, in a non-actuated state (i.e., with noapplied actuation force 160), a surface of the deformable elements 112,120 may each have a substantially planar shape, and the optical lensassembly 100 may be configured and positioned to not substantially alteran image or view passing through the optical lens assembly 100. In otherwords, the non-actuated state may be a substantially zero-optical powerstate.

Although FIG. 1 illustrates separate actuation forces 160 respectivelyacting on both force distributor rings 150 of the proximal and distalsubassemblies 104, 106, the present disclosure is not so limited. Forexample, a single actuation force 160 applied by a single actuator mayact on both force distributor rings 150 of the proximal subassembly 104and of the distal subassembly 106. Thus, the proximal and distalsubassemblies may be jointly or separately actuated, as may beappropriate for different applications.

In some examples, the optical lens assembly 100 illustrated in FIG. 1may be used to reduce or eliminate the negative impact of a phenomenonknown as the “vergence-accommodation conflict.” Traditional AR displaysmay attempt to create the illusion that a virtual object is set at adistance in the real-world environment by displaying virtual images tothe left eye and to the right eye with a relative offset, such that auser’s eyes converge on the desired real-world focal point to align theleft- and right-side virtual images. At the same time, the user’s leftand right eyes also undergo accommodation to bring the respective left-and right-side virtual images into focus. However, the distance of thereal-world focal point may frequently differ from the distance of theaugmented-reality display, causing a difference between the apparentvergence distance and the apparent accommodation distance of a virtualobject. Unfortunately, because the human visual system is adapted to theexpectation that the apparent vergence distance and the apparentaccommodation distance of a real-world object will match, the mismatchfrequently posed by traditional augmented reality systems may confuse auser’s vision, potentially breaking a sense of immersion-or even causingphysical discomfort.

The optical lens assembly 100 illustrated in FIG. 1 may be configured toaddress the vergence-accommodation conflict. For example, an actuationforce 160 from an actuator (e.g., an electromechanical actuator) isshown in FIG. 1 as being applied in a direction toward the user’s eye,such that the proximal deformable optical element 110 forms a convexshape and the distal deformable optical element 118 forms a concaveshape. Conversely, if the actuation force 160 is applied in a directionaway from the user’s eye, the proximal deformable optical element 110may form a concave shape and the distal deformable optical element 118may form a convex shape. Upon actuation in either direction, theproximal deformable optical element 110 may be configured to adjust theuser’s view of an image rendered on the display element 102. The distaldeformable optical element 118 may be configured to substantiallycounteract the adjustments of the proximal deformable optical element110 with respect to the user’s view of a surrounding real-worldenvironment. In other words, the two deformable optical elements 110,118 may together modify the apparent accommodation distance of a virtualobject or scene shown on the display element 102, while reducing oreliminating any distortion of the appearance of the real-worldenvironment through the optical lens assembly 100.

In some examples, the term “electromechanical actuator” may refer to apiezoelectric material or device, an electroactive polymer, anelectrostrictive polymer, a shape memory alloy, a voice coil, apneumatic actuator, an electromagnetic motor (including for example aservo motor, a stepper motor, a DC motor, or a similar motor), ahydraulic actuator, or a combination thereof. In some examples, the term“electroactive” may refer to a property of a material or compositematerial that deforms in response to an application of electrical energy(e.g., a voltage) and may generate electrical energy when strained ordeformed. Example electroactive materials include piezoelectricmaterials, electrostrictor materials, dielectric elastomers, and ionicpolymer conductors. Electroactive materials may function as transducersor as a component of transducers for actuating and deforming thedeformable optical elements 110, 118.

The structural support elements 108, 116 may be or include asubstantially transparent material with a higher relative rigidity thanthe deformable elements 112, 120 and the deformable media 114, 122. Byway of example, the structural support elements 108, 116 may be orinclude one or more of a glass material, a sapphire material, a crystalmaterial (e.g., quartz), a polycarbonate material, another polymermaterial, or a non-polymeric material. The structural support elements108, 116 may provide a protective barrier for the user’s eye, for thedeformable optical elements 110, 118, and for other components of theoptical lens assembly 100 (e.g., the display element 102, an actuator,etc.).

The proximal structural support element 108 may also include aneye-tracking element, which may be configured for estimating aninter-pupillary distance of the user’s eyes, a gaze distance, and/or afocal point. The eye-tracking element, if present, may include aselective-transmission element that transmits light having a selectedproperty and that does not transmit light that does not have theselected property. For example, the proximal structural support element108 may include a coating or material that allows visible light to passwhile reflecting non-visible light (e.g., infrared light). In thisexample, an infrared light source may direct infrared light to theproximal structural support element 108, which may be reflected onto theuser’s eye. An infrared camera may detect infrared light that isreflected from the user’s eye and back to the proximal structuralsupport element 108, to track the user’s eye.

As shown in FIG. 1 , the structural support elements 108, 116 may eachbe a substantially planar element that does not substantially alter animage viewed through the structural support elements 108, 116. In otherembodiments, the structural support elements 108, 116 may include acorrective ophthalmic lens (e.g., a positive-optical power lens, anegative-optical power lens, a lens for correction of an aberration,etc.), or another optical lens element. Optionally, an anti-reflectivecoating may be applied to the structural support elements 108, 116. Theouter periphery of the deformable elements 112, 120 may be directly orindirectly coupled to the respective structural support elements 108,116, which may define cavities therebetween for containing thedeformable media 114, 122.

The deformable elements 112, 120 may include a substantiallytransparent, flexible film of a single material or multiple materials.By way of example and not limitation, the deformable elements 112, 120may include at least one of a polymer material (e.g., a thermosetpolymer, a thermoplastic polymer, an elastomer, a silicone material,polydimethylsiloxane, a polyurethane elastomer, a fluoropolymermaterial, polyvinylidene fluoride or a copolymer thereof, a polyolefinmaterial, a polyacrylate material, etc.), a ceramic material, a glassmaterial, a crystalline (e.g., substantially single-crystal) material,or a composite material. The deformable elements 112, 120 may be orinclude a single material or a multi-layer structure. The deformableelements 112, 120 may include a barrier material for controlling gas orliquid diffusion, an anti-reflective material, or a combination thereof.In some examples, a material of the deformable elements 112, 120 mayinclude a flexible, transparent, water-impermeable material, such asclear and elastic polyolefins, polycycloaliphatics, polyethers,polyesters, polyimides and/or polyurethanes, for example, polyvinylidenechloride films, including commercially available films,

In some examples, and depending on the material and configurationselected for the deformable elements 112, 120, the deformable elements112, 120 may be pre-tensioned to achieve a desired profile and responseto actuation and/or to reduce the negative effects of so-called “gravitysag.” Gravity sag may refer to a lower portion of the deformable opticalelements 112, 120 being thicker on average than an upper portion, due togravity urging the deformable elements 112, 120 and/or deformable media114, 122 downward.

One or both of the deformable elements 112, 120 may have a non-uniformmechanical strain or stress profile when in a non-actuated state.Examples of deformable elements having non-uniform mechanical strain orstress profiles and example methods for achieving non-uniform mechanicalstrain or stress profiles are described below, such as with reference toFIGS. 4-11 .

Referring again to FIG. 1 , the deformable media 114, 122 may be asubstantially transparent material with mechanical properties that allowfor deformation upon actuation of the optical lens assembly 100. By wayof example and not limitation, the deformable media 114, 122 may be orinclude a gas (e.g., air, nitrogen, etc.), a liquid (e.g., water,degassed water, mineral oil, saline solution, a high-refractive indexliquid, etc.), a polymer material, a gel (e.g., a silicone gel), or afoam (e.g., a silica aerogel), etc.

FIG. 2 shows an embodiment of an optical lens assembly 200 similar tothe optical lens assembly 100 described above with reference to FIG. 1 ,but with a curved proximal structural support element 208 and a curveddistal structural support element 216, rather than the substantiallyplanar structural support elements 108, 116 shown in FIG. 1 . Forexample, one or both structural support elements 208, 216 may be orinclude a corrective ophthalmic lens or a curved zero-optical power lens(e.g., a zero-power meniscus lens). A shape of the proximal and/ordistal structural support elements 208, 216 may, in some embodiments, betailored to or selected in consideration of a specific user to correctvision impairments or to otherwise meet user preferences.

In some examples, for realization of a sub-assembly with similarfunctionality to the sub-assembly in FIG. 1 , the structural supportelements 208, 216 in FIG. 2 can be zero-power meniscus lens elements forimproved anti-reflective properties and easier integration withpotentially non-flat optical eye-tracking and/or ophthalmic opticalelements at the proximal structural support element 208. A zero-opticalpower curved lens may provide some advantages over a substantiallyplanar lens for some applications, such as for improved anti-reflectiveproperties and/or improved fit to a user’s facial contours, for example.

The optical lens assembly 200 may include a proximal optical lenssubassembly 204 and a distal optical lens subassembly 206. The proximaloptical lens subassembly 204 may include the proximal structural supportelement 208 and a proximal deformable optical element 210 (including aproximal deformable element 212 and a proximal deformable medium 214).The distal optical lens subassembly 206 may include the distalstructural support element 216, a distal deformable optical element 218(including a distal deformable element 220 and a proximal deformablemedium 222). A display element 202 and the optical lens subassemblies204, 206 may be mounted on a housing 240.

In addition, FIG. 2 illustrates an actuation mechanism different fromthat of the embodiment of FIG. 1 . For example, instead of actuation byan applied actuator force 160 on a force distributor ring 150, thedeformable elements 212, 220 of FIG. 2 may each include an electroactivematerial configured to deform upon application of a sufficient voltageby a driver circuit 270. For example, substantially transparentdielectric elastomers, piezoelectrics including polymers likepolyvinylidene fluoride (“PVDF”) and its copolymers, and/or singlecrystal ceramics like lithium niobate, quartz, K_(0.5) Na_(0.5) NbO₃(“KNN”), barium titanate, lithium niobate, lithium tetraborate, quartz,lead zirconate titanate, Pb(Mg_(⅓)Nb_(⅔))O₃-PbTiO₃, and/orP_(b)(Zn_(⅓)Nb_(⅔))O₃-PbTiO₃, etc. are electroactive materials that maybe included in the deformable elements 212, 220. With dielectricelastomers or other forms of electroactive polymers, for example, thedeformable elements 212, 220 may include rigid or semi-rigid structuralmaterials for load bearing or for reducing or eliminating the level ofpre-tension in the deformable elements 212, 220. In these cases,alternative architectures with a wider range of potential materialselection, material geometries, and boundary conditions may improveperformance and manufacturability.

Additionally, the deformable elements 212, 220 may include electrodesfor electrically coupling the driver circuit 270 to the deformableelements 212, 220. In some examples, the electrodes may be or include asubstantially transparent, electrically conductive material, such as atransparent conducting oxide, indium tin oxide, a nanocompositematerial, carbon nanotubes, silver nanowires, and/or graphene.

FIG. 2 illustrates the optical lens assembly 200 in an actuated state.For example, application of a sufficient voltage and polarity on thedeformable elements 212, 220 by the driver circuit 270 may deform thedeformable optical elements 210, 218. In this example, the proximaldeformable optical element 210 is shown as being deformed into a concaveshape and the distal deformable optical element 218 is shown as beingdeformed into a convex shape. Conversely, the application of asufficient voltage of an opposite polarity to that shown in FIG. 2 mayresult in the proximal deformable optical element 210 forming a convexshape and the distal deformable optical element 218 forming a concaveshape. As discussed above with reference to FIG. 1 , the optical lensassembly 200 may be configured to address the vergence-accommodationconflict.

FIG. 3 illustrates an example HMD 300 (e.g., AR glasses, VR glasses)capable of incorporating the optical lens assemblies described herein.In one example, the HMD 300 may be dimensioned to be worn on a head of auser. The HMD 300 may include a frame element 302 for supporting atleast one deformable optical lens assembly 304 according to the presentdisclosure. In some embodiments, the optical lens assembly(ies) 304 maybe tailored to or selected in consideration of a particular user’s eye.In addition to supporting the optical lens assembly(ies) 304, the frameelement 302 may also support other elements, such as an actuator, adriver circuit for the actuator, a power supply element (e.g., abattery), a communication component (e.g., a component for communicationvia Wi-Fi, BLUETOOTH, near-field communications (“NFC”), etc.), adisplay element, a graphics processing unit for rendering an image onthe display element, an image sensor (e.g., a camera), an eye-trackingelement, etc. As shown in FIG. 3 , the optical lens assembly 304 mayhave an asymmetric shape. In addition, the HMD 300 may have a differentshape and design than is shown in FIG. 3 , such as in the form of a VRheadset or another shape that suits user preferences or a particularapplication. The optical lens assembly(ies) 304 may be or include, forexample, any of the optical lens assemblies or subassemblies describedin this disclosure.

FIG. 4 is a graph 400 that illustrates an example pre-formed profile ofa deformable element according to some embodiments of the presentdisclosure. The deformable element may be thermoformed out of a polymermaterial, such as thermoplastic polyurethane (“TPU”). In the formingprocess, a number of customized thermoforming molds can be used toproduce a variety of stock keeping units (“SKUs”) of deformable elementsor associated optical lens assemblies like the approach used for glassesin the ophthalmics industry. Thus, optical lens assemblies may befabricating to exhibit different sizes, shapes, and/or opticalproperties (e.g., ophthalmic correction values, maximum deformed opticalpowers, optical axis location to account for inter-pupillary distancesfor various users, etc.). For example, cylindrical curvature can beintroduced for astigmatism correction, etc.

The example pre-formed TPU deformable element shown in FIG. 4 may beformed with a non-planar (e.g., curved) mold to result in the profileillustrated in the graph 400. The thermoforming of the deformableelement may result in a central region of the deformable element havinga highest relative elevation, sloping or tapering downward toward anouter periphery of the deformable element, which may have a lowestrelative elevation. The profile shown in the graph 400 may represent ashape of the deformable element upon formation, without application ofan external force (e.g., an actuation force or a stretching force) onthe deformable element. After thermoforming, the deformable element maybe substantially uniformly stretched and fixed to a pre-tensioning ringto hold the pre-tension in the deformable element. By pre-forming thedeformable element to exhibit a non-planar shape as illustrated in thegraph 400 of FIG. 4 , substantially uniform stretching of the deformableelement may result in non-uniform mechanical strain and/or stress.Non-uniform strain and stress in the deformable elements may bedesirable in some examples and applications, such as to counteract thenegative effects of gravity sag or to modify the deformed, actuatedprofile of the associated optical lens assemblies for specific users orsets of users having certain ophthalmic needs (e.g., aberrationcorrections, inter-pupillary distances, etc.). Accordingly, thepre-formed profile of the deformable element may be adjusted tocustomize optical lens assemblies for specific users or groups of users.

FIG. 5 shows a graph 500 of the after-stretch principal strain and FIG.6 shows a graph 600 of the after-stretch von Mises stress in thedeformable element corresponding to the graph 400 of FIG. 4 ,respectively. Due to the pre-forming of the deformable element asdescribed above with reference to FIG. 4 , the stress may vary byapproximately 15% and the strain may vary by approximately 30% across anarea of the deformable optical element. In additional examples, thestrain may vary by at least about 2%, such as by at least about 5%, orby at least about 10%. Accordingly, substantially uniform stretching ofthe pre-formed deformable element may result in non-uniform stress andstrain in the deformable element. By way of example, the principalstrain in the substantially uniformly stretched deformable element maybe lowest (e.g., about 0.106 in the example of FIG. 5 ) in a centralregion of the deformable element and may be highest (e.g., about 0.140in the example of FIG. 5 ) near an outer periphery of the deformableelement. Similarly, the von Mises stress may be lowest (e.g., about 3.2MPa in the example of FIG. 6 ) in the central region and may be highest(e.g., about 4.2 MPa in the example of FIG. 6 ) near the outerperiphery.

Since tension may be introduced by stretching the deformable element toa given size, the pre-tension may be stated in terms of nominalprinciple strain (e.g., 5%, 7%, 10%, 12%, etc.). Since the thicknessdimension of the deformable element may be substantially less than thecorresponding lateral dimensions, the out-of-plane stress may beconsidered negligible in calculating load variability, for example. Asan in-plane stress problem, the load variability across the deformableelement may be given in terms of stress state (e.g., von Mises stressvariability of 5%, 10%, 20%, 30%, etc.) because the in-plane stresseslargely determine the deformation behavior.

The pre-stress condition may scale with the level of pre-tension.Therefore, the applied pre-tension may be variable across the area ofthe deformable element, even though a substantially uniform pre-tensionmay be applied at the outer periphery of the deformable element. Thisvariability can result in a non-uniform stress and/or strain profile forreducing gravity sag by, for example, applying a larger pre-stress nearthe peripheral edge than in a central region, to counteract thegravity-induced pressure change where the effects are largest (e.g.,along a bottom edge of the deformable optical element). Alternatively,if edge effects are of concern, a higher pre-stress may be applied inthe central region for alleviating gravity sag while reducing negativeedge effects. In these cases, the nominal pre-stress or pre-strain maybe less than with uniform tensioning and may be locally larger incertain areas to target gravity sag.

FIG. 7 is a plot 700 showing reaction forces of the deformable opticalelement, which may be approximately equivalent to applied actuationforces. As a dimple height (i.e., a distance from a neutral,non-actuated deformable element to its highest or lowest point afteractuation) increases from 1 mm to 8 mm, for example, the correspondingpre-stress variation may also increase. Embodiments with relativelylarger dimple heights and pre-stress variations may exhibit a reducedactuation force requirement, as illustrated in the plot 700.

Additionally, the pre-stress condition may affect a transient responseof the deformable element to the applied force and displacement of theactuator through a non-uniform mechanical strain or stress profile,which may generally correlate to a stiffness profile. A stiffnessprofile may be tuned to reduce or prevent undesired transient modes forhigh image quality and optical performance during actuation. The plot700 of FIG. 7 compares the reaction forces for upward movement anddownward movement of the optical elements and for various dimpleheights. In HMDs like those shown in FIGS. 1 and 2 , optical lenssubassemblies having respective concave and convex curvatures may besimultaneously obtained upon actuation. During actuation, approximatelyequal and opposite optical powers at the proximal and distal opticallens subassemblies may improve optical quality through the two opticallens subassemblies, including during a transient response when one ofthe lenses is deformed to a concave shape and the other of the lenses isdeformed to a convex shape. Thus, substantially matching the upward anddownward reaction forces, such as by pre-forming the deformable elementsas described above with reference to FIGS. 4-6 , may improve a user’svisual experience during actuation.

FIG. 8 shows a plot 800 illustrating a velocity of the deformableelement as a function of dimple height and time during actuation. Bypre-forming and stretching the deformable element as described above,the height of the dimple can be tuned to modify the transient responsein the downward motion to more closely match that of the upward motion.The plot 800 of FIG. 8 demonstrates how non-uniform pre-stress enablestunability of the transient response for an improved user experience.

Introducing temperature-controlled viscoelastic creep in an elastomericdeformable element is an example approach to obtain a non-uniform andcustomizable pre-stress condition. An elastomer, such as TPU, may beformed and stretched to create a uniformly pre-tensioned deformableelement. Through viscoelastic creep induced in the elastomer viatensioning, a residual strain or stress may be introduced to thematerial. Creep is both stress- and temperature-dependent. Therefore,selective heating with controlled temperature can be applied to induce anon-uniform mechanical strain or stress profile through thermalrealization. In some embodiments, conditioning the deformable elementafter stretching may facilitate customization of the resulting opticallens assembly at a later stage in the manufacturing process. Thisapproach, therefore, facilitates user-specific customization, where theoptical lens assembly can be fully assembled and then selectively heatedto create a non-uniform strain or stress profile for an inter-pupillarydistance or ophthalmic correction specifically tailored to an individualend user, for example.

FIG. 9 is a plot 900 qualitatively depicting a strain contour map of anasymmetric optical lens assembly with a location of an optical axis 904adjusted from a geometric center 902 of the optical lens assembly, suchas for adapting to a user’s inter-pupillary distance and/or forobtaining an axisymmetric strain near the optical axis 904. The distanced illustrated in the plot 900 of FIG. 9 demonstrates a shift of theoptical axis 904 from the geometric center 902 of the optical lensassembly. Accordingly, a desired optical centration location (e.g., alocation of an optical axis at a center of the lens curvature) of theoptical lens assembly may be achieved by employing embodiments of thepresent application. In some embodiments, an axisymmetric strain orstress profile may induce a more axisymmetric deformation profile toreduce astigmatic aberrations. Such a strain or stress profile can beintroduced through the fabrication processes described in thisdisclosure, for example.

FIG. 10 is a flow chart illustrating a method 1000 of fabricating anoptical lens assembly according to embodiments of the presentdisclosure. In operation 1010, a target strain profile may be defined,such as in consideration of a desired optical axis location, dimpleheight, optical properties (e.g., accommodative properties, adaptiveproperties, etc.), shape of the optical lens assembly, inter-pupillarydistance, expected gravity sag, etc. The target strain profile may bedefined to substantially achieve a desired set of optical properties,such as to tailor the resulting optical lens assembly to a specific useror set of users. By way of example, optical ray tracing and finiteelement simulations may be used to define the target strain profile fora specific user or for a set of users over a defined accommodativeoptical power range. In some embodiments, the defined target strainprofile may be induced in a deformable element by performing operations1020, 1030, and 1040, as described below.

In operation 1020, a pre-form profile of the deformable element may beset to substantially achieve the defined target strain profile afterfurther processing. The pre-form profile may be set in consideration offactors such as material properties of the material of the deformableelement, thickness of the deformable element, shape of the deformableelement, etc. Finite element simulations, possibly including iterativeoperations and calculations, may be used to determine the pre-formprofile to achieve the target strain profile.

In operation 1030, the deformable element may be thermoformed to thepre-form profile. For example, a sheet of polymer material may bepositioned on a mold surface having the pre-form profile. The sheet ofpolymer material may be pre-heated or heated on or in the mold to asufficient temperature such that the polymer material may substantiallyform to the shape and contours of the mold surface. The sheet of polymermaterial may be formed to the shape of the mold surface, and the sheetof polymer material may be cooled to a sufficiently low temperature suchthat its molded shape is at least semi-permanent. The molded sheet ofpolymer material may then be removed from the thermoforming mold. If themolded sheet of polymer material is larger than a desired end shape, thesheet of polymer material may be trimmed to the desired end shape.

In operation 1040, the thermoformed deformable element may be stretched.The stretching may be a substantially uniform or non-uniform stretching,depending on the defined target strain profile, material properties ofthe deformable element, shape of the deformable element, desired opticalproperties, etc. In some embodiments, the material of the deformableelement may be uniaxially stretched. In additional embodiments, thematerial of the deformable element may be biaxially stretched, such asalong two substantially perpendicular axes. In some embodiments, thematerial of the deformable element may be stretched along at least oneaxis that is angled from vertical and horizontal relative to an intendedorientation of the resulting optical lens assembly when in use. Forexample, at least some element of the force used to pre-stretch thematerial of the deformable element may be tangential to an edge of thedeformable element. In each of these examples, a pre-tensioning ring maybe coupled to the deformable element to substantially maintain thestretched state of the deformable element when not actuated. Theresulting pre-stretched deformable element may substantially exhibit thetarget strain profile defined in operation 1010.

The pre-strained deformable element may then be directly or indirectlycoupled (e.g., bonded, adhered, coupled via a separate edge sealmaterial, etc.) to a substantially transparent structural supportelement (e.g., a substantially planar lens element, a curved lenselement, etc.). A substantially transparent deformable medium may bedisposed between the deformable element and the structural supportelement. The structural support element, deformable medium, anddeformable element may be coupled to and supported by a housing (e.g., aframe element). An actuator (e.g., an electromechanical actuator, adriver circuit for an electroactive material, etc.) may be coupled tothe housing and to the deformable element to actuate and deform thedeformable optical element, thus altering an optical property of theoptical lens assembly upon actuation.

FIG. 11 is a flow chart illustrating a method 1100 of fabricating anoptical lens assembly according to additional embodiments of the presentdisclosure. In operation 1110, a target strain profile of a deformableelement may be defined, as discussed above with reference to FIG. 10 .In operation 1120, a temperature profile may be set to substantiallyachieve the defined target strain profile. Application of sufficientheat to the deformable element may induce a residual strain or stress inthe deformable element. The temperature profile may include a selectiveapplication of heat, such as different amounts of heat and/or fordifferent lengths of time in different regions of the deformableelement, to substantially achieve the target strain profile. Forexample, finite element simulations, possibly including iterativeoperations and calculations, may be performed to determine theappropriate temperature profile to achieve the target strain profile.

In operation 1130, the deformable element may be stretched, as describedabove with reference to FIG. 10 . The stretched deformable element maybe assembled into an optical lens assembly, such as by coupling thedeformable element to a pre-tensioning ring, directly or indirectlycoupling the deformable element to a structural support element, anddisposing a deformable medium in a cavity defined between the deformableelement and the structural support element.

In operation 1140, heat may be applied to the optical lens assemblyaccording to the set temperature profile to induce a non-uniformmechanical strain or stress in the deformable element according to thedefined target strain profile.

Operations 1150 and 1160 illustrate an alternative (compared tooperations 1130 and 1140 described above) sequence for some proceduresof fabricating an optical lens assembly. Referring to operation 1150,after the temperature profile is set as indicated in operation 1120, thedeformable element may be stretched and heat may be applied to thestretched deformable element according to the set temperature profile.

In operation 1160, the stretched and heat-treated deformable element maybe assembled into an optical lens assembly, such as by coupling thedeformable element to a pre-tensioning ring, directly or indirectlycoupling the deformable element to a structural support element, anddisposing a deformable medium in a cavity defined between the deformableelement and the structural support element. Thus, the set temperatureprofile may be applied to the deformable element at various stages offabricating the optical lens assembly.

In additional embodiments, portions of the material of the deformableelement may be selectively polymerized. For example, in polymers thatare cured by exposure to actinic radiation (e.g., ultraviolet light,X-rays, etc.), the portions of the deformable element may be selectivelyexposed to actinic radiation to selectively polymerize those portions(or to induce additional cross-linking compared to portions that are notexposed to the actinic radiation). The selective polymerization mayinduce a residual strain or stress in the material of the deformableelement.

In some embodiments, deformable elements and/or optical lens assemblieshaving a variety of desired mechanical strain or stress profiles andresulting optical properties may be fabricated according to methods ofthis disclosure. A deformable element and/or optical lens assemblyhaving a desired set of optical properties may be selected from a groupof deformable element and/or optical lens assemblies with respectivedifferent mechanical strain or stress profiles and optical properties.

Accordingly, disclosed are optical lens assemblies and associated HMDsthat include a deformable element that exhibits a non-uniform mechanicalstrain and/or mechanical stress profile. Various methods for achievingthe non-uniform mechanical strain and/or mechanical stress profile arealso disclosed. The disclosed apparatuses and methods may enableimproved optical lens assemblies with desirable deformation responses toactuation, at commercially reasonable costs.

Embodiments of the present disclosure may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., VR, AR, mixed reality(MR), hybrid reality, or some combination and/or derivatives thereof.Artificial reality content may include completely generated content orgenerated content combined with captured (e.g., real-world) content. Theartificial reality content may include video, audio, haptic feedback, orsome combination thereof, any of which may be presented in a singlechannel or in multiple channels (such as stereo video that produces athree-dimensional effect to the viewer). Additionally, in someembodiments, artificial reality may also be associated withapplications, products, accessories, services, or some combinationthereof, that are used to, e.g., create content in an artificial realityand/or are otherwise used in (e.g., perform activities in) an artificialreality. The artificial reality system that provides the artificialreality content may be implemented on various platforms, including anHMD connected to a host computer system, a standalone HMD, a mobiledevice or computing system, or any other hardware platform capable ofproviding artificial reality content to one or more viewers.

The process parameters and sequence of the steps described and/orillustrated herein are given by way of example only and can be varied asdesired. For example, while the steps illustrated and/or describedherein may be shown or discussed in a particular order, these steps donot necessarily need to be performed in the order illustrated ordiscussed. The various example methods described and/or illustratedherein may also omit one or more of the steps described or illustratedherein or include additional steps in addition to those disclosed.

The preceding description has been provided to enable others skilled inthe art to best utilize various aspects of the example embodimentsdisclosed herein. This example description is not intended to beexhaustive or to be limited to any precise form disclosed. Manymodifications, combinations, and variations are possible withoutdeparting from the spirit and scope of the present disclosure. Theembodiments disclosed herein should be considered in all respectsillustrative and not restrictive. Reference should be made to theappended claims and their equivalents in determining the scope of thepresent disclosure.

Unless otherwise noted, the terms “connected to” and “coupled to” (andtheir derivatives), as used in the specification and claims, are to beconstrued as permitting both direct and indirect (i.e., via otherelements or components) connection. In addition, the terms “a” or “an,”as used in the specification and claims, are to be construed as meaning“at least one of.” Finally, for ease of use, the terms “including” and“having” (and their derivatives), as used in the specification andclaims, are interchangeable with and have the same meaning as the word“comprising.”

What is claimed is:
 1. An optical lens assembly, comprising: a pre-strained deformable element that exhibits at least one of a non-uniform mechanical strain or stress profile that is based, at least in part, on an inter-pupillary distance of a user; a structural support element coupled to the pre-strained deformable element; and a deformable medium positioned between the pre-strained deformable element and the structural support element.
 2. The optical lens assembly of claim 1, wherein the non-uniform mechanical strain or stress profile is a result of a variable pre-tension applied to the pre-strained deformable element.
 3. The optical lens assembly of claim 1, wherein the non-uniform mechanical strain profile is a result of residual stress within the pre-strained deformable element.
 4. The optical lens assembly of claim 1, wherein the non-uniform mechanical strain profile has a variability of at least about two percent.
 5. The optical lens assembly of claim 1, wherein the non-uniform mechanical stress profile has a variability of at least about five percent.
 6. The optical lens assembly of claim 1, wherein the optical lens assembly is positioned in a head-mounted display.
 7. The optical lens assembly of claim 6, wherein the head-mounted display comprises augmented-reality glasses.
 8. The optical lens assembly of claim 1, wherein the non-uniform mechanical strain or stress profile is configured to at least one of: correct for at least a portion of a cylindrical error of a user’s eye; or counter gravity sag in the pre-strained deformable element.
 9. The optical lens assembly of claim 1, further comprising a display element positioned adjacent to the pre-strained deformable element, such that the display element is viewable by the user through the pre-strained deformable element.
 10. The optical lens assembly of claim 1, further comprising a display element positioned proximate to the pre-strained deformable element.
 11. A method of fabricating an optical lens assembly, the method comprising: inducing at least one of a non-uniform mechanical strain or stress profile in a deformable element, wherein the non-uniform mechanical strain or stress profile is based, at least in part, on an inter-pupillary distance of a user; positioning the deformable element over a structural support element; and disposing a deformable medium between the deformable element and the structural support element.
 12. The method of claim 11, wherein inducing the non-uniform mechanical strain or stress profile in the deformable element comprises at least one of: conditioning a material of the deformable element; or stretching the material of the deformable element.
 13. The method of claim 12, wherein conditioning the material of the deformable element comprises thermoforming a polymer to a non-planar profile.
 14. The method of claim 12, wherein conditioning the material of the deformable element comprises at least one of: selectively exposing portions of the material of the deformable element to heat to induce residual strain or stress in the material of the deformable element; or selectively polymerizing portions of the material of the deformable element to induce residual strain or stress in the material of the deformable element.
 15. The method of claim 12, wherein stretching the material of the deformable element comprises at least one of: uniaxially stretching the material of the deformable element; biaxially stretching the material of the deformable element; or stretching the material of the deformable element along at least one axis that is angled from vertical and horizontal relative to an intended orientation of the optical lens assembly when in use.
 16. A method of fabricating an optical lens assembly for a user, the method comprising: providing a deformable element that is substantially transparent; inducing at least one of a non-uniform mechanical strain or stress profile in the deformable element, wherein the non-uniform mechanical strain or stress profile of the deformable element is selected based, at least in part, on an inter-pupillary distance of the user; and positioning the deformable element over a structural support element.
 17. The method of claim 16, further comprising disposing a deformable medium between the deformable element and the structural support element.
 18. The method of claim 16, further comprising determining the inter-pupillary distance of the user, wherein: inducing the non-uniform mechanical strain or stress profile in the deformable element is performed before determining the inter-pupillary distance of the user; and providing the deformable element comprises selecting the deformable element with the induced non-uniform mechanical strain or stress profile from a group of deformable elements with respective different mechanical strain or stress profiles.
 19. The method of claim 16, wherein positioning the deformable element over a structural support element comprises positioning the deformable element over a substantially transparent structural support element.
 20. The method of claim 16, wherein inducing the non-uniform mechanical strain or stress profile in the deformable element comprises at least one of: stretching a material of the deformable element; thermoforming the material of the deformable element to a non-planar profile; or selectively exposing portions of the material of the deformable element to heat to modify residual strain or stress in the material of the deformable element. 